UNIVERSITY    OF    CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,  CALIFORNIA 


THE  CODLING  MOTH  IN  WALNUTS 


H.  J.  QUAYLE 


BULLETIN  402 

April,  1926 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1926 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/codlingmothinwal402quay 


THE  CODLING  MOTH  IN  WALNUTS' 

H.  J.  QUAYLE2 


INTRODUCTION 

The  codling  moth,  Carpocapsa  pomonella  Linn.,  has  been  known  to 
attack  the  English  or  Persian  walnut  (Juglans  regia)  in  California 
since  1909.^  In  1913,  Mr.  C.  W.  Beers,  Horticultural  Commissioner  of 
Santa  Barbara  County,  sent  the  writer  a  quantity  of  walnuts  infested 
with  a  larva  which  proved  to  be  that  of  the  codling  moth.  During  the 
same  season  walnuts  in  the  vicinity  of  Santa  Ana  were  found  to  be 
infested  with  the  same  pest.  These  appear  to  be  the  first  actual 
records  of  injury  to  walnuts  by  the  codling  moth  in  southern  Cali- 
fornia, although  walnut  growers,  including  Roy  K.  Bishop,  then 
Horticultural  Commissioner  of  Orange  County,  recall  having  seen 
similarly  infested  nuts  earlier  than  1913.  At  that  time,  in  Santa 
Barbara  and  Orange  counties,  less  than  one  per  cent  of  the  crop  was 
affected.  An  increase  followed,  with  yearly  fluctuations,  and  by  1918 
the  infestation  had  become  serious. 

The  Citrus  Experiment  Station  at  once  undertook  studies  looking 
toward  the  control  of  the  pest.  At  the  instance  of  the  California 
Walnut  Growers'  Association,  a  special  appropriation  was  made  by 
the  Legislature.  This  appropriation  was  made  payable  to  the  State 
Commission  of  Horticulture  and  through  its  director,  Mr.  G.  H.  Hecke, 
one-half  of  the  amount  was  turned  over  to  the  University  for  investi- 
gational work,  while  one-half  was  retained  by  Mr.  Hecke 's  office  for 
quarantine  and  survey  work. 

In  1908  C.  P.  Lounsbury,  Chief  of  the  Division  of  Entomology, 
Union  of  South  Africa,  first  noted  the  occurrence  of  the  codling  moth 
in  walnuts^  in  Wellington  and  Worcester,  Cape  Province.     In  the 


1  Paper  No.  143,  University  of  California,  Graduate  School  of  Tropical  Agri- 
culture and  Citrus  Experiment  Station,  Eiverside,  California. 

2  During  a  portion  of  the  years  1919,  1920,  and  1921  Roy  K.  Bishop,  and  for  a 
portion  of  the  year  1920,  George  H.  Vansell  and  Paul  R.  Kerrick,  assisted  in  this 
investigation. 

3  Foster,  S.  W.,  On  the  nut-feeding  habits  of  the  codling  moth,  U.  S.  Dept. 
Agr.,  Bur.  Ent.,  Bull.  805;  ....     1910. 

4  Mally,  C.  W.,  Codling  moth  in  Walnuts,  South  African  Fruit  Grower,  3:3. 
1916.  See  also:  Lounsbury,  C.  P.,  Worms  in  v^alnuts.  South  African  Fruit 
Grower  and  Small  Holder,  6:307.     1919. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

following  years  the  infestation  increased  rapidly  and  during  the 
season  of  1914-15  Mally  reported  an  infestation  amounting  to  50  or 
60  per  cent  of  the  crop  in  some  parts  of  the  Oudtshoorn  district.  In 
France  the  codling  moth  has  been  known  to  attack  walnuts  since  1859. 
It  was  originally  considered  to  be  a  distinct  species  {Carpocapsa 
putaminana  Stand.)  but  later  was  determined  as  a  variety  of  pomo- 
nella  L.,  the  species  which  attacks  the  apple.  Mr.  Carl  Heinrich,  of 
the  U.  S.  Bureau  of  Entomology,  states  in  correspondence  his  opinion 
that  the  insect  attacking  the  walnut  in  Europe  is  not  a  variety,  but  is 
the  same  form  as  that  which  occurs  in  the  apple  in  the  United  States. 


IDENTITY  OF  THE  SPECIES 

Several  experiments  were  carried  out  in  order  to  determine  the 
behavior  of  the  insect  when  transferred  from  the  apple  to  the  walnut, 
and  vice  versa.  Eggs  which  had  been  deposited  on  apples  were  trans- 
ferred to  walnuts;  a  normal  number  hatched,  and  the  larvae  bored 
into  the  walnut  in  the  same  manner  as  on  the  original  host.  Recently 
hatched  larvae  which  had  begun  to  feed  on  the  apple  were  transferred 
to  the  walnuts  and  these  also  developed  normally.  The  same  was  true 
with  half-grown  and  nearly  mature  larvae.  In  whatever  stage  the 
codling  moth  larvae  from  the  apple  was  transferred  to  the  walnut, 
the  change  of  food  had  no  effect  on  their  development.  Similar 
transfers  were  made  of  larvae  from  the  walnut  to  the  apple,  with 
similar  results. 

The  next  step  was  to  determine  the  behavior  of  the  moth  as  to  her 
choice  between  depositing  eggs  on  the  walnut  and  the  apple.  Moths 
which  had  been  reared  from  the  apple  were  liberated  in  cages  where 
apples  and  walnuts  were  suspended.  These  moths  deposited  eggs  with 
equal  freedom  on  either  apples  or  walnuts.  In  fact,  eggs  were  laid  on 
various  other  fruits,  including  the  lemon,  although  fruits  with  a  fuzzy 
surface,  such  as  the  peach,  were  generally  avoided.  Then  moths  that 
had  been  reared  from  the  walnut  were  tested  in  the  same  way  as  those 
from  the  apple  and  these  also  showed  no  preference  in  egg  laying. 

Since  the  above  experiments  were  carried  out  in  cages  only  two  feet 
square,  it  was  deemed  advisable  to  work  under  more  nearly  natural 
conditions.  Accordingly,  tests  were  made  on  two  walnut  trees  of  fair 
size  enclosed  under  cheesecloth.  This  furnished  conditions  as  nearly 
normal  as  practicable  while  confining  known  moths  to  particular  trees. 
For  each  walnut  on  these  two  trees  there  was  suspended  an  apple,  in 
most  cases  in  direct  contact  with  the  nut.    Under  one  tree  pupae  from 


Bull.  402] 


TPIE    CODLING    MOTH    IN    WALNUTS 


the  apple  were  liberated,  and  under  the  other,  pupae  from  the  walnut. 
In  both  cases  eggs  were  deposited  indiscriminately  on  both  apples  and 
walnuts.  The  larvae,  however,  seemed  to  show  some  preference  for 
the  apple,  since  some  larvae  which  hatched  on  the  walnut  moved  over 
to  and  entered  the  apple. 

Three  other  walnut  trees  were  enclosed  in  cheesecloth  cages, 
12  X  12  X  18  feet  (see  fig.  1).  In  one  of  these  cages  codling  moth  pupae 
from  the  walnut  were  liberated;  in  another,  pupae  obtained  locally 
from  the  apple,  and  in  the  third,  pupae  obtained  from  the  apple  four 


Fig.  1.     One  of  the  walnut  trees  enclosed  in  cheesecloth  cage 
in  oviposition  experiments. 


hundred  miles  away.  Nuts  on  all  of  these  trees  were  attacked, 
although  more  were  infested  on  the  tree  where  the  pupae  came  from 
the  walnut.  This  greater  infestation  was  due,  in  part  at  least,  to  the 
better  condition  of  the  pupae  obtained  from  the  walnut.  Approxi- 
mately the  same  number  of  pupae  were  liberated  in  each  of  the  trees, 
but  mold  had  developed,  particularly  in  those  obtained  from  the  apple 
four  hundred  miles  distant,  because  they  had  been  kept  in  a  cool 
basement  to  delay  their  emergence. 

There  is  nothing  in  the  foregoing  experiments  to  indicate  that  the 
codling  moth  which  infests  walnuts  is  a  different  species  or  variety 
from  that  which  infests  the  apple,  although  some  special  adaptation 
to  the  walnut  may  be  necessary.  Critical  examination  of  the 
morphology  of  the  different  stages  also  indicated  no  specific  or  varietal 


6  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

differences.  Under  field  conditions,  however,  the  behavior  of  the 
insect  seems  to  be  somewhat  different  from  that  indicated  in  our 
control  experiments.  It  has  been  noted  that  where  the  branches  of 
walnut  and  apple  trees  were  in  close  proximity  (in  some  cases  inter- 
woven) a  heavy  infestation  occurred  in  the  apple  and  only  a  slight  or 
no  infestation  in  the  walnut.  These  facts  have  been  noted  within  the 
area  where  it  is  well  known  that  the  codling  moth  attacks  the  walnut. 
Numerous  cases  might  be  cited  outside  of  the  areas  where  walnuts 
were  infested,  where  apples  were  heavily  infested  while  walnuts  grow- 
ing in  close  proximity  were  entirely  free  from  attack.  Apples  infested 
with  codling  moth  occur  throughout  the  walnut-growing  area,  but 
except  in  two  or  three  limited  areas,  the  codling  moth  is  not  at  present 
a  pest  of  economic  importance  on  the  walnut,  and  there  are  large 
walnut-growing  areas  where  the  codling  moth  has  not  yet  been  found 
on  the  walnut. 

Where  the  walnut  is  not  known  to  be  infested,  occasional  infested 
nuts  are  most  likely  to  be  found  in  close  proximity  to  apple  trees.  For 
example,  until  1921  the  codling  moth  was  unknown  in  walnuts  in 
Ventura  County,  but  the  writer  found  a  few  infested  nuts  in  two 
different  localities  in  that  county,  and  in  both  cases  apple  trees  were 
growing  in  close  proximity  to  the  walnuts.  Similar  cases  have  been 
observed  outside  of  the  well  known  infested  areas  in  Orange  County. 

The  insect  undoubtedly  has  come  to  the  walnut  from  the  apple. 
For  this  reason  many  growers  desire  to  remove  apple  trees  from  their 
dooryards;  others  have  suggested  the  planting  of  apples  among  the 
walnut  trees  as  a  trap  crop.  We  believe  nothing  practical  can  be 
gained  by  either  removing  the  apple  trees  or  extending  their  planting. 


LIFE  HISTORY^  AT  SANTA  ANA 
Wintering  Larvae 

The  larvae  hibernate  in  cocoons  beneath  the  loose  bark  in  old 
pruning  cuts,  under  bands,  in  trays,  and  in  other  places  in  which  they 
can  find  protection.  Only  very  rarely  do  they  remain  in  the  nuts. 
They  are  inactive  until  early  spring,  when  they  remodel  their  cocoons 
so  as  to  furnish  exit  tubes  for  the  moths. 

Spring  hrood  of  pupae. — In  1920,  an  average  season,  counts 
and  estimates  made  in  the  field  on  April  6  indicated  that  about  10  per 
cent  of  the  wintering  larvae  in  the  walnut  and  about  15  per  cent  of 

5  Tables  showing  the  life  history  of  the  codling  moth  in  great  detail  can  be 
found  in  various  publications.     Only  a  summary  of  our  data  is  given  here. 


Bull.  402]  tj^^    codling   MOTH   IN    WALNUTS  7 

those  in  the  apple  had  pupated.  On  April  19,  about  20  per  cent  had 
pupated  from  the  walnut  and  30  per  cent  from  the  apple.  The  last 
pupation  of  this  brood  from  the  walnut  occurred  on  June  19  and  from 
the  apple  about  10  days  earlier.  The  duration  of  this  stage  varies 
from  18  to  30  days. 

Spring  hrood  of  moflis. — The  first  moths  of  the  season  were  seen  in 
the  field  on  April  15  in  1919,  and  on  April  24  in  1920.  The  maximum 
emergence  was  about  June  1*^  and  the  last  emergence  record  for  the 
apple  was  June  20,  and  for  the  w^alnut  June  30. 

The  First  Generation 

First  hrood  of  eggs. — The  first  eggs  observed  on  the  walnut  in  the 
field  in  1919  were  seen  on  May  8.  In  1920,  eggs  were  first  seen  on 
pears,  May  8,  on  apples.  May  12,  and  on  walnuts.  May  14.  The 
maximum  number  of  eggs  were  present  on  the  apple  about  June  1,  and 
on  the  walnut  about  June  10.  It  has  been  noted  that  eggs  are  deposited 
earlier  on  the  apple  than  on  the  walnut,  and  that  eggs  of  this  brood 
continue  to  be  deposited  until  early  in  July.  The  incubation  period 
varies  from  10  to  20  days. 

First  hrood  of  larvae. — Hatching  of  eggs  was  first  observed  on 
May  14.  The  greatest  number  of  larvae  appeared  on  walnuts  during 
the  second  or  third  week  of  June.  A  large  majority  of  the  first-brood 
larvae  enter  or  attempt  to  enter  the  calyx  end  of  the  nut.  Before  all 
of  this  brood  enter,  however,  the  nut  becomes  too  hard  at  the  calyx  end 
(third  week  of  June)  and  entrance  is  thereafter  sought  at  other 
points,  particularly  where  two  nuts  are  in  contact.  The  larvae  remain 
in  the  nuts,  on  the  average,  about  35  days.  Some  of  this  brood  were 
found  in  the  nuts  69  days  after  entrance,  and  even  then  they  showed 
no  signs  of  spinning  a  cocoon  until  disturbed  and  induced  to  spin 
by  cracking  the  nuts.  Such  cases  were  noted  late  in  August.  An 
occasional  larva  of  this  brood  even  passes  the  winter  before  transform- 
ing. Definite  cases  of  wintering  of  this  brood  have  been  noted  at 
Carpinteria  as  well  as  at  Santa  Ana. 

First  hrood  of  pupae. — The  first  pupation  of  larvae  hatched  in  the 
spring  was  observed  on  June  15.  The  majority  of  this  brood  pupated 
during  the  latter  half  of  July.  The  period  spent  in  the  cocoon  varied 
from  6  days  to  several  weeks,  but  most  of  the  specimens  transformed 
in  10  to  12  days. 

6  Where  the  year  is  not  given,  the  data  will  be  understood  to  be  the  average 
(or  extreme)  for  the  years  1919,  1920,  and  1921. 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

First  hrood  of  moths. — The  appearance  of  moths  from  eggs  laid  in 
the  spring  began  on  June  25,  reached  a  maximum  by  July  30,  and 
continued  until  September  1  or  later.  Moths  from  the  spring  brood 
were  still  present  on  June  25,  so  there  is  an  overlapping  of  broods  that 
persists  and  becomes  more  pronounced  as  the  season  advances.  In 
fact,  the  overlapping  may  continue  into  the  following  season,  since 
larvae  of  two  or  three  diffeernt  broods  may  pass  the  winter  together. 

The  dates  given  for  the  first  observed  appearance  of  the  eggs, 
larvae,  pupae  and  adults  do  not  necessarily  refer  to  the  same  insect, 
nor  do  they  represent  the  first  actual  appearance  of  the  different 
stages,  but  only  the  '^ observed"  appearance.  For  example,  the  moth 
that  emerged  on  June  25  may  have  pupated  earlier  than  June  20,  the 
date  of  the  first  observed  pupation.  The  maximum  emergence  of  this 
brood  occurred  about  July  30.  The  average  length  of  life  of  the  moth 
is  about  two  weeks. 

The  Second  Generation 

Second  hrood  of  eggs. — During  the  last  week  of  June  and  the  first 
two  weeks  of  July,  egg-laying  is  at  a  minimum,  although  occasional 
eggs  are  deposited  during  this  period.  The  first  eggs  of  the  second 
brood  were  seen  on  July  3.  By  the  third  week  of  July,  eggs  become 
more  numerous,  and  the  peak  of  egg-laying  by  this  brood  is  during 
the  first  or  second  week  of  August. 

Second  hrood  of  larvae. — Second-brood  larvae  began  to  appear 
early  in  July  and  reached  their  maximum  numbers  the  second  and 
third  weeks  of  August.  One  larva  which  hatched  on  July  30,  pupated 
on  August  18;  this  period  (20  days)  represented  the  shortest  larval 
life  observed.  On  the  other  hand,  under  the  heading  ''First  Brood 
of  Larvae,"  a  record  is  given  of  69  days  in  the  larval  stage.  Many  of 
the  second-brood  larvae  pass  the  winter  as  such,  and  do  not  complete 
their  development  until  the  following  year. 

Second  hrood  of  pupae  and  moths.- — Some  of  the  second-brood 
larvae  transform  to  the  pupa  and  adult,  the  first  of  which  may  appear 
the  last  week  of  August  and  continue  to  appear  until  October. 

The  Third  Generation 

Third  hrood  of  eggs  and  larvae. — Eggs  and  young  larvae  of  this 
partial  brood  appear  in  September  and  October.  Recently  hatched 
larvae  have  been  observed  to  enter  the  nuts  as  late  as  the  second  week 
in  October.  When  the  nuts  are  harvested,  though  most  of  the  larvae 
are  fully  developed,  many  are  in  earlier  stages. 


Bull.  402] 


THE    CODLING   MOTH    IN    WALNUTS 


SEASONAL  HISTORY  AT  SANTA  ANA 

The  wintering  larvae  in  their  cocoons  begin  to  change  to  pupae 
late  in  March  and  continue  to  pupate  until  the  middle  of  June.  The 
first  moths  appear  during  the  middle  of  April,  the  peak  of  emergence 
occurs  about  June  1  and  the  last  of  the  brood  has  emerged  by  July  1. 
The  peak  of  egg-laying  by  this  spring  brood  of  moths  occurs  the  first 
or  second  week  of  June,  while  the  first  week  of  May  and  the  first  week 
of  August  respectively  represent  the  beginning  and  the  end  of  the 
brood.  The  peak  of  the  appearance  of  the  larvae  occurs  about  June  15, 
while  May  15  and  July  15  represent,  respectively,  the  beginning  and 


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Fig.  2.    Diagram  illustrating  the  seasonal  history  of  the  codling  moth 
in  walnuts  at  Santa  Ana. 

the  end  of  the  brood.  The  peak  of  the  appearance  of  the  moths  of  the 
first  brood  occurs  the  first  week  of  August.  Second-brood  eggs  appear 
in  maximum  numbers  about  August  10.  Second-brood  larvae  appear 
the  second  and  third  week  of  August,  and  second-brood  moths  about 
September  15.  Eggs  and  larvae  of  the  third  generation  appear  in 
September  and  October  (fig.  2).  The  wintering  larvae  include  those  of 
the  first,  second,  and  third  broods.  There  is  thus  but  one  complete 
generation  of  the  insect  with  a  partial  second  and  third  generation. 


SEASONAL  HISTORY  AT  CARPINTERIA 

While  an  occasional  moth  may  appear  at  Carpinteria  almost  as 
early  in  the  season  as  at  Santa  Ana,  the  great  majority  appear  later, 
In  1919  the  peak  of  appearance  of  the  spring  brood  of  larvae  occurred 
during  the  first  and  second  weeks  of  July.  In  1920  the  peak  occurred 
about  the  third  week  in  June.     There  is  only  a  partial  second  brood 


10 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


of  larvae  at  Carpinteria,  and  so  far  as  observed,  no  third  brood.  At 
Santa  Ana  the  greatest  amount  of  injury  is  done  by  the  second-brood 
larvae  in  late  July,  in  August,  and  in  early  September,  while  at 
Carpinteria  the  greatest  injury  is  done  by  the  first  brood  during  the 
latter  part  of  June  and  in  July  and  August.  Nuts  containing  the 
first -brood  larvae  were  collected  in  July,  and,  while  some  of  the  larvae 
transformed  to  the  adult,  some  remained  in  their  cocoons  throughout 
the  following  winter.  There  is  thus  only  one  complete  generation  of 
the  insect  at  Carpinteria  and  a  partial  second  generation.  Differences 
in  temperature  between  Carpinteria  and  Santa  Ana  (fig.  3)  account 
for  the  difference  in  the  seasonal  history  of  the  codling  moth  at  the 
two  places. 


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Fig  3.  Average  monthly  mean  temperatures  for  years  1919,  1920,  and  1921. 
Solid  line  represents  Santa  Ana  and  dotted  line,  Santa  Barbara.  Note  the 
difference  in  mean  temperature  from  May  to  September,  inclusive,  the  active 
season  for  the  codling  moth.  This  accounts  for  the  difference  in  life  history 
of  the  insect  at  the  two  places. 


INSECTS  LIKELY  TO  BE  MISTAKEN  FOR  THE 
CODLING  MOTH 

Two  insects  which  attack  the  walnut  may  be  mistaken  for  the 
codling  moth.  One  of  these,  the  fruit  tree  leaf-roller  {Archips 
argyrospila  Walt.),  attacks  the  growing  nut,  and  the  other,  the  Indian- 
meal  moth  {Plodia  inter punctella  Hbn.),  attacks  the  nut  only  in 
storage.     The  larva  of  the  fruit-tree  leaf-roller  bores  into  the  nut  in 


Bull.  402] 


THE    CODLING   MOTH   IN    WALNUTS 


11 


much  the  same  manner  as  the  larva  of  the  codling  moth.  The  two 
larvae  are  of  about  the  same  size,  but  the  larva  of  the  leaf -roller  when 
feeding  in  walnuts  is  cream  colored  while  that  of  the  codling  moth  is 
more  frequently  pink  when  full-grown.  The  fruit-tree  leaf-roller 
occurs  only  occasionally  on  walnuts;  hence  its  control  is  not  thus  far 
a  problem,  but  in  new  localities  its  work  may  be  mistaken  and  it  may 
thus  be  reported  for  the  more  serious  codling  moth.  In  one  case,  for 
example,  a  few  walnut  trees  growing  in  a  dooryard  showed  a  high 
percentage  (20  per  cent)  of  infestation  by  this  moth. 


\^^ 

^ 


Fig.  4.     Development  of  walnut,  showing  the  closing  and 
shriveling  of  the  stigma. 

The  codling  moth  never  breeds  in  storage,  and,  aside  from  rare 
hibernating  specimens,  it  is  not  found  in  stored  nuts  except  soon  after 
harvesting.  The  worm  that  is  most  commonly  found  in  the  nuts  in 
storage  is  the  Indian-meal  moth.  This  insect  is  frequently  troublesome 
in  storage,  but  it  may  be  destroyed  by  heating  the  nuts  to  a  tempera- 
ture of  130-140  degrees  for  one  hour,  or  by  fumigation  with  carbon 
disulphide. 


FEEDING  HABITS  IN  WALNUTS 

Most  of  the  larvae  which  appear  in  the  early  spring  enter  the  nut 
at  the  calyx  end  when  the  nuts  are  small  and  the  stigma  is  still  fleshy 
and  cleft,  as  shown  in  the  smallest  nut  on  the  left  of  figure  4.  Later, 
however,  the  cleft  portion  closes  and  becomes  brown  and  shriveled.  The 
stigma  furnishes  suitable  protection  for  the  larva  while  it  is  entering 
the  nut,  and  hence  entrance  is  sought  at  this  point.  Tables  1  to  4  on 
page  17  give  definite  data  on  the  proportion  of  larvae  entering  at 
the  calyx.    The  calyx  end  is  the  point  where  the  shell  of  the  nut  first 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

hardens.  Hence,  after  about  the  third  week  in  June,  entrance  cannot 
be  effected  at  this  point,  although  attempts  may  be  made  throughout 
the  season.  As  the  nuts  become  larger,  they  often  come  in  contact  with 
one  another,  since  two  or  more  generally  occur  together,  and  the  point 
of  contact  furnishes  a  favorite  place  for  the  larvae  to  enter  throughout 
the  rest  of  the  season  (fig.  5).  The  young  larvae  frequently  make 
several  shallow  burrows  at  this  point  of  contact  and  sometimes  they 
eat  over  the  surface  generally  without  making  a  distinct  burrow. 


Fig.  5.     The  commonest  place  of  entrance  of  the  codling  moth  in 
walnuts  is  where  two  nuts  are  in  contact  as  shown. 

If  the  shell  of  the  nut  has  not  hardened,  the  larvae  penetrate 
directly  through  the  husk  and  shell  to  the  interior.  After  about  the 
middle  of  July,  the  entire  shell  of  the  nut  becomes  so  hard  that  the 
larvae  cannot  burrow  their  way  through,  in  which  case  feeding  con- 
tinues on  the  husk  adjacent  to  the  shell.  A  more  or  less  wandering 
burrow  may  be  made  until  the  fibrous  suture  at  the  base  or  stem  end 
is  found,  where  entrance  may  be  effected  regardless  of  the  hardness 
of  the  shell.  Sometimes  the  burrow  leads  directly  to  the  suture,  but 
in  other  cases  there  is  no  definite  direction  taken.  Occasionally  the 
suture  is  not  found,  and  the  larvae  completes  its  development  by  feed- 
ing entirely  on  the  husk.  Larvae  have  sometimes  been  found  to 
burrow  for  a  considerable  distance  down  into  the  stem  of  the  nut. 
Larvae  emerge  from  the  nut  generally  through  the  suture  at  the  base. 
The  earliest  first-brood  larvae  may  emerge  through  the  shell  of  the 
nut  (fig.  7). 


Bull.  402] 


THE    CODLING    MOTH    IN    WALNUTS 


13 


Fig.  C.     Walnuts  infested  with  the  codling  moth. 


Fig.  7.  The  four  nuts  to  the  left  show  exit  holes  of  codling-moth  larva;  the 
upper  center  nut  shows  an  exit  hole  made  by  an  early  first-brood  larva  in  June, 
before  the  shell  had  hardened.  After  the  shell  hardens  the  only  exit  is  through 
the  basal  suture.  The  two  nuts  on  the  right  show  that  the  larva  has  entered  at 
the  suture,  but  has  not  emerged.  Such  nuts  show  no  entrance  burrow,  but  they 
may  be  distinguished  by  the  presence  at  the  suture  of  small  brown  pellets. 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


VARIETIES  OF  WALNUTS  ATTACKED 

While  all  varieties  of  the  English  walnut  are  attacked  by  the 
codling  moth,  there  is  some  evidence  that  ''hard-shells"  and  such 
budded  varieties  as  the  Placentia  may  be  somewhat  more  susceptible 
than  the  average  soft-shell  type.  The  Eureka  seems  to  be  the  least 
invested.  Some  nuts  are  much  more  tightly  sealed  than  others  and 
hence  it  is  more  difficult  for  the  larvae  to  enter  them.  "Hard-shells" 
have  a  flattened  base  and  a  wide  suture.  Placentias  are  characterized 
as  loosely  sealed  nuts.  Eurekas,  on  the  other  hand,  are  firmly  sealed 
and,  while  there  is  individual  variation,  some  Eurekas  are  so  closely 
sealed  at  the  base  that  codling  moth  larvae  cannot  effect  an  entrance. 
In  addition  to  its  common  food  plants,  the  codling  moth  has  been 
found  in  the  field  in  apricots  and  in  one  case  a  considerable  infestation 
in  oranges  that  were  growing  close  by  a  walnut  drying  house. 

Since  it  is  the  larvae  entering  the  nuts  in  July  and  later  that  do 
the  most  conspicuous  injury,  nuts  which  are  tightly  sealed  at  the  base 
are  least  often  infested.  Such  nuts  will  not  necessarily  be  free  from 
attack,  since  the  larva  will  feed  on  the  husk  in  any  case,  but  fewer 
worms  will  actually  enter  the  nut,  and  so  long  as  the  feeding  is  con- 
fined to  the  husk  the  nut  is  not  materially  affected.  Most  of  the 
larvae  of  the  second  brood,  and  all  those  of  the  later  broods,  as  well 
as  some  of  the  first  brood  w^hich  attack  the  nut  in  the  cooler  sections 
after  about  the  middle  of  July,  cannot  gain  entrance  to  the  nut  except 
through  the  fibrous  suture  at  the  base. 


AMOUNT  OF  INFESTATION 

When  the  attention  of  the  Station  was  first  called  to  the  infestation 
of  walnuts  by  the  codling  moth  in  1913,  counts  made  in  the  most 
heavily  infested  orchards  at  Carpinteria  showed  an  infestation  of  less 
than  1  per  cent.  Between  1913  and  1918  there  was  marked  yearly 
fluctuation,  but,  aside  from  a  few  individual  orchards,  the  degree  of 
infestation  had  not  become  serious  before  1918.  In  1918,  however, 
there  was  a  marked  increase,  and  growers  placed  the  infestation  as 
high  as  50  per  cent  in  particular  orchards.  From  1919  we  have 
authentic  records  of  the  amount  of  infestation,  and  the  highest  average 
record  for  a  single  season  in  any  orchard  is  37  per  cent.  In  this 
particular  orchard  in  the  same  season  45  per  cent  of  the  first  picking 
was  infested.    In  1918  some  orchards  may  have  exceeded  even  this 


Bull.  402] 


THE    CODLING   MOTH   IN    WALNUTS 


15 


figure  for  the  first  picking,  which,  if  true,  would  account  for  the  high 
percentage  recorded  by  certain  growers. 

During  the  year  1919,  however,  the  infestation  reached  its 
highest  point  in  the  Santa  Ana  district  as  a  whole.  A  marked  decrease 
occurred  in  1920,  and  in  1921  the  infestation  was  scarcely  severe 
enough  to  justify  the  expense  of  control  measures.  The  three-year 
records  for  the  orchards  in  this  district  treated  under  my  supervision 
follow : 


Percentage  of  Infestation  in  Check  Plots   (Without  Control  Measures), 

Santa  Ana 


Year 

Orchard  A 

Orchard  B 

Orchard  C 

Orchard  D 

1919  ... 

16.1 

6.3 
1.5 

9.8 

6.3 
3.1 

12.0 
6.1 
1.1 

12.1 

1920 

22.0 

1921 

3.6 

In  1924  the  infestation  at  Carpinteria  was  as  high  as  in  any  season 
since  the  codling  moth  appeared  in  walnuts.  In  Orange  County  in 
the  same  year  the  infestation  had  become  so  reduced  as  to  make  control 
work  unnecessary  except  on  one  property. 

At  Rivera  in  Los  Angeles  County  the  infestation  in  1924  was  as 
high  as  22  per  cent  in  some  orchards.  The  infestation  here  had 
increased  rapidly  between  1922  and  1924.  A  general  campaign  of 
control  was  then  inaugurated  under  the  supervision  of  the  Los  Angeles 
County  Horticultural  Commissioner.  In  1925  there  was  a  marked 
decrease  in  the  infestation. 

Thus,  it  will  be  seen  that  there  is  considerable  seasonal  fluctuation 
and  local  variation  in  the  amount  of  codling  moth  infestation  in 
walnuts.  As  is  well  known,  there  are  seasonal  fluctuations  of  the 
codling  moth  in  apples,  but  there  has  been  no  general  decrease  in 
infestation  of  the  apple  to  a  point  where  treatment  has  been 
unnecessary. 

The  section  of  Orange  County  where  the  codling  moth  was  first 
abundant  was  where  control  work  first  became  unnecessary.  Another 
section  where  the  peak  of  infestation  appeared  a  few  years  later  was 
the  last  to  require  treatment.  Carpinteria  is  the  chief  section  where 
the  codling  moth  has  maintained  about  a  uniform  infestation  through- 
out the  period  of  observation,  that  is  from  1918  to  1925.  Prediction 
cannot  be  made  that  the  codling  moth  may  not  increase  again  in 
Orange  County  or  that  it  may  not  decrease  in  Carpinteria.  It  seems 
safe  to  assume,  however,  that  the  walnut  is  not  the  favorite  host  for 


16  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

the  codling  moth  and  for  that  reason  greater  fluctuations  in  infestation 
may  be  expected  than  with  the  apple. 

It  is  sometimes  maintained  that  measures  should  be  applied  regu- 
larly and  continuously  throughout  a  district  from  the  time  the  first 
worms  are  found  in  order  to  prevent  any  development  of  infestation, 
rather  than  reduce  the  infestation  after  it  has  started.  The  writer 
does  not  recommend  such  a  program,  however.  Control  measures 
according  to  the  best  practice  at  present  will  allow  three  or  four  per 
cent  of  worms  to  escape  if  conditions  in  the  particular  area  are  at  all 
favorable  for  the  development  of  the  moth.  When  the  infestation 
does  not  exceed  two  or  three  per  cent,  control  measures  will  not 
decrease  materially  this  amount  of  infestation.  There  are  thousands 
of  acres  of  walnuts  where  the  codling  moth  has  been  known  to  occur 
for  the  past  eight  or  ten  years,  but  where  without  the  use  of  control 
measures  there  has  been  practically  no  increase  in  the  amount  of 
infestation.  The  application  of  control  measures  during  this  period  in 
such  areas  would  have  involved  an  unprofitable  expenditure.  With 
certain  newly  introduced  insects  that  are  sure  to  become  serious  pests, 
control  work  cannot  be  started  too  soon.  In  the  case  of  the  codling 
moth  in  walnuts  the  increase  of  the  insect  has  been  erratic,  since  it  has 
reached  the  status  of  an  economic  pest  (that  is  three  or  four  per  cent  or 
greater  infestation)  in  only  a  limited  part  of  the  total  walnut  area 
known  to  be  infested.  In  Contra  Costa  County,  where  this  insect  was 
first  found  on  walnuts,  it  is  only  rarely  that  a  nut  has  been  found 
infested.  Clearly,  it  would  have  been  false  economy  to  have  treated 
all  the  trees  in  that  section  every  year  since  1909.  Pest  control  work 
must  be  considered  solely  on  an  economic  basis,  although,  of  course, 
more  than  an  immediate  crop  must  be  taken  into  consideration,  since 
the  health  of  the  tree  or  the  possible  effect  on  subsequent  crops  may 
justify  treatment  at  once. 

DROPPING  OF  NUTS 

Most  of  the  nuts  that  are  attacked  by  May  or  early  June,  drop 
from  the  tree  while  still  immature.  Those  attacked  later  are  also 
more  likely  to  drop  than  sound  nuts,  and  the  first  harvest  therefore 
always  shows  a  heavier  percentage  of  infestation  than  later  pickings. 
The  percentage  of  nuts  dropped  during  the  seasons  of  1920  and  1921 
was  much  less  than  in  1919  because  the  first  brood  of  worms  was 
smaller  in  1920  and  1921  than  in  1919. 

A  systematic  effort  was  made  in  1920  to  record  all  nuts  that 
dropped  under  certain  trees  (tables  1  to  4).    These  data  follow: 


Bull.  402] 


THE   CODLING   MOTH   IN    WALNUTS 


17 


TABLE  1 

Maybury  Orchard — Lot  7,  50  trees 


Date  picked 

June 
14 

June 

22 

July 
3 

July 
16 

July 
22 

July 
28 

Totals 

Number  of  fallen  nuts      .    . 

44 
6 

14 
6 
5 

99 
12 
12 
11 
10 

391 

28 

7 

26 

14 

194 

22 

11 

9 

7 

178 

15 

8 
5 

7 

102 
5 
5 

2 
1 

1008 

Number  infested 

88 

Per  cent  infested 

9 

Worms  in  nuts 

59 

Blossom-end  entrance 

44 

TABLE  2 
Brown  Orchard — 30  trees 


Date  picked 

June 
16 

June 

24 

July 
2 

July 
9 

July 
15 

July 
21 

Totals 

Nnmher  of  fallen  nuts 

157 
35 
22 
29 
30 

270 
58 
21 
50 
41 

535 

126 

23 

94 

92 

448 
57 
12 
21 
16 

468 

48 
13 
18 
17 

301 

19 

6 

5 

5 

2179 

Number  infested 

344 

Per  cent  infested 

15 

Worms  in  nuts 

Blossom-end  entrance 

217 
201 

TABLE  3 

Stevens  Orchard — 50  trees 


Date  picked 

June 
4  and  7 

June 
17 

June 
25 

July 
land  2 

July 
15 

July 
21 

July 
26 

Totals 

Number  of  fallen  nuts 

385 
16 
41 
12 
15 

646 
98 
15 

77 
79 

874 
222 
25 
176 
135 

1331 

228 

17 

168 

126 

983 

115 

12 

52 

53 

454 

37 

8 

6 

10 

475 
9 
2 
1 
4 

5148 

Number  infested  .         .    . 

725 

Per  cent  infested 

14 

Worms  in  nuts 

492 

Blossom-end  entrance 

422 

TABLE  4 
Crookshank  Orchard — 40  trees 


Date  picked 

June  25 

July  6 

July  13 

Totals 

Number  of  fallen  nuts 

322 
60 
18 
43 
45 

327 
79 
24 
57 
46 

234 

40 

17 

7 

14 

903 

Number  infested                    

179 

Per  cent  infested 

19 

Worms  in  nuts                                   .    . 

107 

Blossom-end  entrance  

105 

18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

It  will  be  noted  that  the  heaviest  drop  due  to  the  codling  moth 
occurred  late  in  June  and  early  in  July.  It  is  important  to  remember 
in  this  connection  that  various  factors  may  cause  walnuts  to  drop 
prematurely,  and  that  only  where  the  nuts  are  found  to  be  infested, 
but  otherwise  sound,  can  the  drop  be  attributed  to  the  codling  moth. 
Where  both  blight  and  codling  moth  occur,  the  dropping  of  the  nuts 
may  be  due  to  either  or  both.  Of  these  tAVO  causes,  the  blight  is  very 
much  more  serious  than  the  codling  moth.  It  will  also  be  noted  from 
the  figures  given  that  a  larger  percentage  of  the  larvae  entered  at  the 
calyx  in  the  earlier  than  in  the  later  pickings.  On  some  of  the  trees 
for  which  records  were  kept  the  infestation  was  reduced  by  treatment 
for  the  codling  moth. 

DISTRIBUTION  IN  CALIFORNIA 

The  codling  moth  has  been  found  in  all  of  the  walnut  districts  of 
Orange  County,  with  the  heaviest  infestation  occurring  about  Santa 
Ana  and  Tustin.  It  also  occurs  in  Los  Angeles  County  in  the  Whittier- 
Puente-Covina  districts,  with  the  heaviest  infestation  in  certain 
orchards  near  Los  Nietos  and  Rivera.  It  occurs  occasionally  in  the 
Chino  district  in  San  Bernardino  County.  In  Santa  Barbara  County 
it  occurs  most  abundantly  in  the  vicinity  of  Carpinteria.  An  occa- 
sional nut  has  been  found  to  be  infested  in  the  Goleta  district  in  the 
same  county.  A  few  infested  nuts  have  been  seen  in  Casetas  Pass, 
Ventura  County,  where  walnuts  and  apples  are  growing  in  close 
proximity.  A  light  infestation  occurs  near  Saticoy  in  Ventura  County. 
Here  also  the  first  walnuts  found  infested  in  1921  were  growing  close 
to  apple  trees.  A  few  codling-moth  infested  nuts  have  been  found  at 
Arlington  in  Riverside  County. 

PARASITES  AND  PREDATORS 

There  are  a  number  of  parasites  and  predators  that  attack  the 
codling  moth  in  its  different  stages.  The  commonest  egg  parasite  is 
Trichogamum  minutum  Riley.  Eggs  harboring  this  parasite  (there 
are  commonly  three  in  each  egg)  may  be  distinguished  by  their  darker 
color.  From  the  time  the  codling  moth  larva  hatches  until  it  has  bored 
into  the  nut  it  is  exposed  to  the  attacks  of  a  number  of  predatory 
enemies  including  insects,  spiders,  and  birds.  After  it  has  emerged 
from  the  nut  and  while  it  is  in  the  cocoon  the  larva,  and  later  the  pupae, 
are  attacked  by  several  parasites  such  as  Aenoplex  carpocapsa  Cush- 


Bull.  402]  the  codling  moth  in  walnuts  19 

man  and  a  number  of  predatory  insects  such  as  carabid  and  clerid 
beetle  larvae  (fig.  8).  Any  factor  that  helps  to  reduce  the  number  of 
worms  which  attempt  to  enter  the  nuts  is  an  aid  in  control  in  con- 
junction with  the  arsenical  applied;  but  seldom,  if  ever,  are  the 
parasitic  and  predatory  enemies  of  the  codling  moth  important  enough 
in  themselves  to  effect  a  satisfactory  control.  Mr.  Stanley  E.  Flanders, 
entomologist  for  the  Saticoy  Walnut  Growers'  Association,  is  making 
a  special  study  of  the  parasites  of  the  codling  moth  and  the  details  of 
this  subject  will  be  left  for  treatment  by  Mr.  Flanders. 


Fig.  8.     A  predaceous  larva,  Cermatydera  sp.  (Family  Cleridae) 
that  attacks  the  codling  moth  in  its  cocoon. 


CONTROL 

Banding  the  trees  and  picking  up  the  infested  nuts  are  two  possible 
methods  of  control  which  have  been  given  attention.  Picking  up  the 
infested  nuts,  in  our  experience,  did  not  reduce  the  amount  of  subse- 
quent infestation  enough  to  justify  the  expense  of  the  work.  The 
figures  given  in  tables  1  to  4  show  that  less  than  10  per  cent  of  the 
nuts  on  the  ground  harbored  larvae.  During  seasons  and  in  sections 
where  walnut  blight  is  more  prevalent,  the  per  cent  of  worms  in  the 
nuts  on  the  ground  would  be  much  less.  Banding  the  trees  is  recom- 
joaended  as  an  auxiliary  to  spraying  and  also  as  a  means  of  partial 


20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


control  where  the  infestation  is  not  severe  enough  to  warrant  spraying. 
Burlap  cut  a  foot  wide  and  doubled  when  placed  around  the  tree 
makes  a  satisfactory  band.  It  may  be  held  in  place  by  two  finishing 
nails  driven  into  the  tree  trunk.  If  the  bark  is  particularly  rough  it 
is  best  to  smooth  it  in  order  to  make  a  more  suitable  place  for  the 
larvae  to  make  their  cocoons.  The  bands  should  be  in  place  by  June  15, 
and  removed  every  ten  days  or  two  weeks  until  October  15  to  kill  the 
larvae  and  pupae  when  they  may  be  taken  off  for  the  winter.  Most 
of  the  codling  moth  larvae  or  pupae  may  be  detected  at  the  points 
where  the  bands  stick  to  the  tree.  Crushing  is  the  simplest  method 
of  killing  them. 

There  is  but  one  thoroughly  satisfactory  method  for  controlling 
the  codling  moth,  viz.,  to  coat  the  nuts  with  some  poison  which  will 
destroy  the  larvae  before  entrance  is  effected.  The  poison  may  be 
applied  as  a  dust  or  as  a  spray.  Our  further  discussion  of  the  control 
of  the  codling  moth  will  have  to  do  with  these  two  methods. 


Results  of  Dusting  in  1919 

In  1919  a  survey  was  made  of  the  infested  areas  at  Santa  Ana  and 
Carpinteria  in  which  extensive  applications  of  arsenate  of  lead  applied 
as  a  dust  had  been  made.  More  than  200,000  nuts,  representing  some 
5000  pounds,  were  examined.  Counts  were  made  with  each  picking 
in  most  cases,  and  data  representing  the  percentage  of  infestation  were 
obtained  from  over  100  orchards,  about  one-half  of  which  had  been 
dusted.    A  general  summary  of  the  results  is  given  in  table  5. 


TABLE 


Percentage  of  nuts  infested 

Santa  Ana 

Carpinteria 

General  average  of  all  orchards  dusted 

4.73 

6.33 

10.00 

21.9 

.8 

.33 

4.2 

General  average  of  orchards  not  dusted 

9.7 

Highest  percentage  in  any  orchard  dusted  

6.6 

Highest  percentage  in  any  orchard  not  dusted 

15.8 

Lowest  percentage  in  any  orchard  dusted  

.7 

Lowest  percentage  in  any  orchard  not  dusted 

.8 

In  considering  the  data  given  in  table  5,  it  seems  fair  to  assume 
that  most  of  the  heavily  infested  orchards  had  been  dusted.    This  wa$ 


Bulk  402> 


THE    CODLING   MOTH    IN    WALNUTS 


21 


certainly  the  case,  at  least  at  Carpinteria.  One  orchard  well  toward 
the  center  of  the  infested  area  in  that  section,  however,  was  left 
untreated,  and  another  was  not  treated  until  very  late  in  the  season. 
These  two  orchards  alone  Avere  used  in  arriving  at  the  percentage  of 
infestation  (9.7)  in  the  undusted  groves  of  Carpinteria.  Counts  made 
just  outside  the  infested  district  at  Carpinteria  showed  practically  no 
infestation,  whether  the  trees  had  been  dusted  or  not. 


Fig.  9.     Dusting  walnuts  for  the  codling  moth. 


At  Santa  Ana,  however,  many  orchards  that  were  not  dusted 
occurred  among  the  dusted  orchards  in  the  general  area  of  infestation. 
Approximately  an  equal  number  of  determinations  were  made  also 
between  dusted  and  undusted  orchards,  so  that  the  figures  should  be 
fairly  reliable. 


22  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION    ' 

The  experience  with  dusting  in  1919  indicated  that  when  there  was 
a  considerable  infestation  the  treatment  paid,  but  that  where  the 
infestation  was  light,  that  is,  under  three  or  four  per  cent,  the  cost  of 
the  treatment  was  not  returned  in  the  extra  amount  of  sound  nuts 
secured. 

In  order  to  determine  the  relative  merits  of  spraying  and  dusting, 
certain  orchards  were  divided  into  plots  and  treated  under  my  super- 
vision. The  results  for  1919  are  given  in  table  6 ;  the  results  for  1920 
are  given  in  diagrams  1  to  4,  and  in  tabular  form  in  table  7. 

TABLE  6 

Percentage  of  Infestation  in  Sprayed  and  Dusted  Plots  in  1919 


Spra 


Orchard  A 

Sprayed  July  3 1         D  usted  July  3 1                 Check 

6.0                      12.1                     16.1 

Orchard  B 

Sprayed  May  21 
^ed  May  21            and  July  17            Sprayed  July  17 

Check 

3.4                       2.1                       4.5 

9.8 

Orchard  D 

Sprayed  July  23        Dusted  June  13                 Check 

7.1                       9.5                      12.1 

As  is  shown  by  the  above  results,  as  well  as  by  other  data,  the  best 
time  to  give  the  treatment  for  the  codling  moth  in  walnuts  is  from 
the  last  week  of  May  to  the  third  week  of  June.  Allowance  should  be 
made  in  the  above  results  for  the  variations  in  time  of  treatment,  but, 
in  spite  of  the  unfavorable  dates  of  application,  the  figures  are  in 
favor  of  the  spray. 


Bull.  402] 


THE    CODLING   MOTH    IN    WALNUTS 


23 


TABLE  7 
Tabular  Summary — Spraying  and  Dusting/  1920 


Orchard 
A 

Orchard 
B 

Orchard 

c 

1.1 

1.3 

1.1 

3.0 

3.5 

5.2 

6.10 

6.30 

6.10 

157 

70 

60 

7.85 

3.50 

3.00 

4.86 

1.96 

0.54 

0.74 

0.56 

0.40 

0.75 

0.37 

0.38 

10 

4.9 

5 

33 

23 

18 

1.96 

0.87 

0.75 

1.21 

0.49 

0.13 

1.22 

0.31 

0.35 

0.46 

0.12 

0.25 

18.30 

6.90 

11.40 

6.20 
2.40 
3.80 

7.00 

5.00 

12.00 

Orchard 
D 


Infestation  with  one  spraying  (per  cent) 

Infestation  with  one  dusting  (per  cent) 

Infestation  of  check  plots  (per  cent) 

Average  production  per  tree  (pounds) 

Increase  in  sound  nuts  per  tree  by  one  spraying, 

(pounds) 

Increase  in  sound  nuts  per  tree  by  one  dusting 

(pounds) 

Cost  of  spraying  per  tree 

Cost  of  dusting  per  tree 

Amount  of  dust  per  tree  (pounds) 

Amount  of  spray  per  tree  (gallons) 

Increased  value  of  nuts  per  tree,  at  25  cents  per 

pound,  due  to  spraying 

Increased  value  of  nuts  per  tree,  at  25  cents  per 

pound,  due  to  dusting 

Net  returns  per  tree  from  one  spraying 

Net  returns  per  tree  from  one  dusting 

Net  returns  per  acre  from  one  spraying 

Net  returns  per  acre  from  one  dusting 

Net  difference  per  acre  in  favor  of  spray.. 


3.7 
10.5 
22.00 
60 

11.00 

6.90 
0.45 
0.44 
6 
20 

2.75 

1.72 

2.30 

1.28 

46.00 

25.60 

20.40 


7  The  cost  figures  represent  what  was  actually  paid  for  the  materials 'used  and 
for  the  work  done  in  1920  on  the  following  basis:  arsenate  of  lead  dust,  6  cents 
per  pound;  arsenate  of  lead  used  in  spray,  25  cents  per  pound;  charge  for  apply- 
ing dust,  8  cents  to  15  cents  per  trees;  charge  for  applying  spray,  1^2  cents  per 
gallon. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


COMPAKISON  OF  SPRAYING  AND  DUSTING,  1920 

Diagram  1 

Orchard  A — 15  acres 

Location  of  Plots,  and  Treatments  and  Percentages  of  Infested  Nuts 


Dusted 

Dusted 

Sprayed 

Dusted 

June  1 

June  1 

June  1 

July  8 

July  8 

E,8% 

3.2^ 

1.3^ 

4/a 

\ 

Sprayed 

Check 

>s^^ 

June  1 

^ 

July  9 

6.355 

Sprayed 

July  9 

3'^ 

Bull.  402J 


THE    CODLING   INLOTII    IN    WALNUTS 


25 


Diagram  2 

Orchard  B — 15  acres 

Location  of  Plots,  and  Treatments  and  Percentages  of  Infested  Nuts 


Sprayed 

Dusted 

June   15 

June  18 

1.3^J 

3.5^ 

Check 
6.3fo 

Dusted 
June   18 

5%  arsenate 
of  lead 

Sprayed 
June   15 
July  9 

Dusted 
June   18 
July  9 

3.3^ 

Ifo 

2.4^ 

Diagram  3 

Orchard  C — 10  acres 

Location  of  Plots,  and  Treatments  and  Percentages  of  Infested  Nuts 


Dusted 

Sprayed 

Dusted 

Sprayed 

June 

June  2 

June   11 

June  10 

5.2^ 

1.1^ 

Che  ok 
6.  If, 

z.rfo 

1.1^ 

Dusted 

Sprayed 

Dusted 

Sprayed 

June   2 

June   2 

June   11 

June   10 

July   17 

July  10 

July  17 

July  10 

5.6fo 

.6% 

4.9^ 

*9fo 

26 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


Diagram  4 

Orchard  D — 10  acres 

Location  of  Plots,  and  Treatments  and  Percentages  of  Infested  Nuts 


Sprayed 
June  10 

Dusted 
June  9 

3.75S 

Check 
ZZfo 

10,5?J 

Sprayed 
June  10 
July  12 

■ 

Dusted 
June   9 
July  10 

3.9fo 

8.9^ 

Results  in  1921 

The  four  orchards  indicated  in  the  diagrams  and  in  the  tabular 
statement  for  1920  received  the  same  treatments  in  1921,  except  that 
the  sprayed  and  dusted  plots  were  interchanged.  The  infestation  was 
so  light  in  1921,  however,  that  the  variation  in  the  figures  was  too 
small  to  be  reliable ;  hence  the  data  for  that  year  are  omitted. 


Discussion  of  Dusting  versus  Spraying 

The  data  presented  consistently  indicate  that  spraying  is  more 
effective  than  dusting  for  the  codling  moth  in  walnuts.  The  cost  of 
spraying  is  not  much  greater,  and  sometimes  is  less  than  that  of 
dusting.  The  proper  basis  on  which  to  judge  any  method  of  control 
is  that  afforded  by  the  ' '  net  returns, ' '  and  it  is  here  that  the  advantage 
of  spraying  is  most  pronounced,  as  is  shown  by  the  data  presented. 


Bull.  402]  THE   CODLING   MOTH   IN    WALNUTS  27 

There  is  another  consideration  of  importance,  the  rapidity  with 
which  a  given  acreage  can  be  treated.  As  regards  the  actual  time 
employed,  this  point  is  very  much  to  the  advantage  of  dusting.  Dust- 
ing is,  however,  greatly  restricted  by  weather  conditions,  so  that  the 
difference  in  acreage  covered  by  the  two  methods  in  one  season  is  not 
so  great  as  might  at  first  appear.  Wind,  even  if  very  light,  interferes 
with  dusting,  and  this  is,  of  course,  a  variable  factor.  Dusting  opera- 
tions are  restricted  to  a  few  hours  in  the  early  morning,  while  spraying 
may  usually  be  continued  throughout  the  day. 

On  account  of  their  large  size,  walnut  trees  have  been  considered 
unsuitable  for  spraying,  not  only  because  of  the  difficulty  of  covering 
the  highest  trees,  but  because  of  the  large  quantity  of  spray  required. 
The  first  of  these  objections  has  been  overcome  by  the  recent  develop- 
ments in  high-power  spray  outfits.  Through  the  courtesy  of  the  Bean 
Spray  Pump  Company  we  secured  the  loan  of  the  first  super-giant 
machines  manufactured  by  that  concern.  In  fact,  this  machine  was 
designed  to  meet  the  particular  demands  of  walnut  spraying.  Such 
a  machine  (figs.  10  and  11)  can  maintain  a  pressure  of  300  pounds 
with  two  spray  guns  that  will  throw  the  spray  to  the  top  of  the 
highest  walnut  tree.  The  same  type  of  machine  is  now  (1925)  very 
generally  manufactured  and  used  for  all  kinds  of  spraying  work.  The 
ordinary  larger  power  spray  outfits  are  also  fairly  satisfactory  but 
only  one  gun  can  be  used  when  large  trees  are  sprayed. 

Another  objection  to  spraying,  namely  the  quantity  of  spray 
required,  seems  important  when  the  amount  required  per  tree  is  con- 
sidered. It  is  true  that  large  trees  will  require  40  gallons,  while  for 
trees  of  average  size  the  amount  will  be  about  25  gallons.  But  the 
proper  standard  of  comj^arison  for  spraying,  as  well  as  for  returns 
on  the  crop,  etc.,  is  cost  per  acre  or  amount  of  land  involved.  Most 
authorities  are  agreed  that  mature  walnut  trees  should  stand  not  less 
than  60  feet  apart,  which  would  make  about  12  trees  to  the  acre. 
Fifty  feet  apart  is  the  minimum,  and  at  this  distance  there  would  be 
only  17  trees  to  the  acre.  Twelve  walnut  trees  requiring  35  gallons 
of  spray  each  would  require  420  gallons  of  spray.  An  acre  with  60 
apple  trees  requiring  8  gallons  of  spray  each  would  require  480  gallons 
of  spray.  An  acre  with  90  citrus  trees  requiring  10  gallons  of  spray 
each  would  require  900  gallons  of  spray.  Thus,  the  quantity  of  spray 
required  on  an  acre  basis  presents  no  more  serious  a  problem  with 
walnuts  than  with  fruit  trees  such  as  the  apple  or  orange ;  furthermore 
while  apples  may  require  as  many  as  five  applications,  one  application 
or  two  will  suffice  for  the  same  pest  in  the  walnut. 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  10.     Spraying  walnut  trees.     Nozzle  adjusted  for  spraying 
upper  part  of  tree. 


Bull.  402J 


THE    CODIJNG    MOTPI    IN    WAT.NUTS 


29 


Fig.  11.     Spraying  walnut  trees  for  codling  moth.    Nozzle  adjusted 
for  spraying  lower  part  of  tree. 


30  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Material  and  Amount  to  Use 

A  large  acreage  was  dusted  in  1919  in  both  Santa  Ana  and  the 
Carpinteria  district,  with  the  standard,  or  acid,  arsenate  of  lead. 
After  a  few  weeks  the  walnut  foliage  began  to  show  characteristic 
arsenical  burning  and  this  burning  continued  to  increase  as  the  season 
advanced.  In  my  own  tests  during  the  same  year  only  basic  or  neutral 
arsenate  of  lead  was  used,  since  previous  experience  in  walnut  spray- 
ing indicated  that  walnut  foliage  is  very  susceptible  to  spray  injury. 
No  injury  resulted  from  the  basic  lead  arsenate ;  consequently,  for  the 
second  dusting  that  year,  basic  arsenate  of  lead  only  was  recommended 
and  the  acid  arsenate  of  lead  was  withdrawn  from  the  market  so  far 
as  walnut  dusting  or  spraying  was  concerned.  In  1920  a  single 
orchard  was  sprayed  with  acid  arsenate  of  lead,  and  the  same  severe 
burning  occurred  as  during  the  previous  year. 

In  1925  a  brand  of  basic  arsenate  of  lead  not  previously  used  was 
applied  in  the  Rivera  section.  Arsenical  burning  appeared  in  several 
of  the  orchards.  This  particular  arsenate  of  lead  showed  0.45  per 
cent  water  soluble  arsenic,  but  yielded  a  considerable  amount  of 
soluble  arsenic  when  treated  with  strong  ammonia.  During  and 
after  the  time  of  the  application  there  was  foggy  weather  and  a  few 
showers  of  rain.  Such  conditions  are  favorable  for  arsenical  injury. 
Other  brands  of  arsenate  of  lead  used  in  the  same  section,  and  in  a 
few  cases  in  the  same  orchard,  produced  no  signs  of  injury.  The 
writer's  conclusion  is  that  any  brand  of  basic  arsenate  of  lead  that 
does  not  meet  the  ammonia  test^  is  unsafe  on  walnut  trees  in  the 
coastal  districts  of  California. 

Basic  arsenate  of  lead  is  not  so  poisonous  as  the  acid  form  and  this 
is  a  disadvantage  to  the  walnut  grower.  However,  the  injury  due  to 
''stings"  or  small  burrows  made  by  the  larvae  before  the  weaker 
poison  becomes  effective  is  not  very  important  in  the  case  of  the 
walnut  because  it  occurs  in  the  husk  and  does  not  affect  the  nut.  A 
suitable  amount  to  use  is  5  pounds  to  100  gallons  of  water.  The  dust 
as  usually  received  by  the  grower  is  ready  to  apply.  Self -mixing  dust 
machines  are  in  use,  however,  and  a  considerable  saving  in  cost  is 
effected  by  the  use  of  such  machines.  In  the  case  of  nicotine  greater 
efficiency  is  obtained  if  the  dust  is  made  immediately  before  applying, 
as  is  the  case  with  the  self -mixing  machines.  With  arsenate  of  lead 
however  long  standing  of  the  arsenical  and  carrier  produces  no 
deterioration. 


8  Gray,  Geo.  P.  and  Firman  Thompson,  Economic  poisons,  California  State 
Dept.  Agr.,  Sp.  Publ.  58:12.     1924. 


Bull.  402]  tjj^    CODLING   MOTH   IN    WALNUTS  31 

Experiments  were  made  Avith  dust  containing  2,  5,  10,  and  15  per 
cent  of  arsenate  of  lead,  but  15  per  cent  seems  to  be  the  most  satis- 
factory proportion.  For  a  filler  or  carrier,  kaolin,  hydrated  lime, 
and  the  refuse  lime  from  beet-sugar  factories  have  been  used. 

The  amount  of  dust  required  to  the  tree  is  about  10  pounds  for  the 
largest  trees  and  6  pounds  for  trees  of  average  size.  Fifteen  per  cent 
of  the  weight  of  the  dust  is  arsenate  of  lead,  hence  when  10  pounds  is 
applied  to  a  tree  there  will  be  IV2  pounds  of  arsenate  of  lead.  If  6 
pounds  is  applied  there  w^ill  be  %o  of  a  pound  of  the  arsenate.  When 
the  spray  contains  5  pounds  of  arsenate  of  lead  to  100  gallons  of  water, 
the  tree  receiving  35  gallons  of  spray  will  receive  1%  pounds  of 
arsenate  of  lead.  A  tree  receiving  25  gallons  of  spray  (the  same  sized 
tree  should  receive  at  least  6  pounds  of  dust  or  %o  pound  of  arsenate 
of  lead)  will  receive  l\i  pounds  of  arsenate  of  lead.  Whether  spraying 
or  dusting  is  employed,  the  object  is  to  get  the  necessary  amount  of 
arsenate  of  lead  on  the  tree.  Eighty-five  per  cent  of  the  weight  of  the 
dust  in  the  85-15  combination,  and  all  of  the  water  in  the  spray,  are 
merely  carriers  and  have  no  insecticidal  value. 

It  is  important  to  cover,  so  far  as  is  practicable,  every  nut  on  the 
tree  with  the  arsenical.  Other  parts  of  the  tree  should  also  be  covered 
if  aphis  is  being  sprayed  for  at  the  same  time.  Our  data  show  that 
there  is  less  infestation  of  the  codling  moth  in  the  upper  than  in  the 
lower  part  of  the  walnut  tree ;  nevertheless,  the  upper  part  of  the  tree 
should  be  covered.  At  the  present  time  spraying  has  been  the  com- 
mercial practice  employed  in  all  of  the  codling  moth  infested  groves 
in  the  Carpinteria  district  excepting  one  where  dust  is  applied  with  a 
self -mixing  dust  machine.  At  Rivera  the  next  most  important  district 
from  the  standpoint  of  codling  moth  infestation,  spraying  has  been 
used  exclusively.  At  Saticoy  where  there  is  a  light  infestation  dusting 
has  been  used  exclusively. 

Codling-Moth  and  Aphis  Control  Combined 

Where  it  is  necessary  to  control  the  walnut  aphis  {Chromaphis 
juglandicola  Kalt),  it  so  happens,  according  to  the  writer's  conclusion, 
that  the  time  practically  coincides  with  the  time  for  the  treatment  of 
the  codling  moth,  namely,  during  the  last  week  of  May  and  the  first 
two  or  three  weeks  of  June.  Hence,  for  the  control  of  the  aphis  and 
codling  moth,  it  is  only  necessary  to  combine  40  per  cent  nicotine 
sulfate  with  the  arsenate  of  lead.  For  spraying  use  10  pounds  of  basic 
arsenate  of  lead  and  from  %  to  %  of  a  pint  of  40  per  cent  nicotine 


32  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

sulfate  to  200  gallons  of  water.  For  dusting,  the  amounts  are  15 
pounds  of  arsenate  of  lead,  1  to  2  pounds  of  40  per  cent  nicotine 
sulfate,  and  a  carrier  to  make  100  pounds.  In  some  years,  particularly 
in  Santa  Barbara  County,  aphis  control  may  be  necessary  before  the 
proper  time  for  the  codling-moth  treatment.  The  walnut  aphis  is  one 
of  the  easiest  of  the  aphids  to  kill  with  nicotine.  Since  a  liberal 
amount  of  dust  is  necessary  for  the  codling  moth,  the  amount  of 
nicotine,  whether  in  spray  or  dust,  may  be  less  than  that  necessary  for 
aphis  control  work  alone. 

Aphis  Control  Alone 

Two  per  cent  nicotine  dust^  is  the  most  satisfactory  material  for 
the  walnut  aphis.  The  amount  of  dust  per  tree  may  be  much  less 
than  that  used  for  the  codling  moth;  ordinarily,  2  to  5  pounds  per 
tree  is  sufficient.  During  the  latter  part  of  May  and  the  first  part 
of  June  is  the  best  time  to  make  the  application.  If  the  treatment  be 
postponed  as  long  as  possible,  but  given  before  any  important  injury 
is  done,  the  trees  will  be  protected  against  infestation  later  in  the 
season. 

A  spray  may  be  used  giving  satisfactory  results  also  against  the 
walnut  aphis.  For  this  purpose  a  mixture  of  1 2  to  %  pint  of  40  per 
cent  nicotine  sulfate  and  4  or  5  pounds  of  soap  to  200  gallons  of  water 
is  recommended. 

Number  of  Applications 

The  results  given  for  1919  and  1920  indicated  no  advantage  in 
making  more  than  one  application  of  spray  or  dust.  However,  when 
the  infestation  is  severe  or  the  broods  of  larvae  are  irregular  a  second 
application  is  desirable.  The  time  for  making  a  second  application  is 
the  latter  part  of  July  or  early  in  August. 

Time  of  Application 

The  time  of  treatment  is  based  on  the  appearance  of  the  first  brood 
of  larvae  in  the  nuts.  They  commence  to  enter  the  nuts  early  in  May, 
but  at  this  time  the  nuts  are  so  small  that  a  spray  applied  then  would 
become  so  thinly  distributed  as  the  nut  grows  as  to  be  ineffective. 
Something  may  be  gained  by  an  early  application  in  getting  the  spray 
more  effectively  into  the  stigma,  which  is  open  or  parted  at  this  time 


9  A  material  originated  by  R.  E.   Smith,   consisting  simply  of  40  per  cent 
nicotine  sulphate  incorporated  into  a  carrier. 


Bull.  402]  tjjj.    codling   MOTH   IN    WALNUTS  33 

(see  fig.  4),  but  this  advantage  is  more  han  offset  by  the  small  size 
of  the  nuts.  The  peak  of  appearance  of  the  first-brood  larvae  in  the 
Santa  Ana  district  occurs  during  the  second  or  third  week  of  June. 
Hence,  the  period  of  treatment  there  should  begin  during  the  last  week 
in  May  and  end  about  the  third  week  in  June.  The  development  of 
the  codling  moth  varies  in  different  seasons.  For  example,  my  own 
control  work  at  Santa  Ana  in  1919  was  started  on  May  25,  in  1920  on 
June  1,  and  in  1921  on  June  8.  There  is  thus  seasonal  variation,  but 
this  is  not  so  great  as  to  make  the  control  ineffective  if  the  work  is 
carried  on  during  the  period  indicated.  In  the  case  of  the  apple,  the 
time  for  the  calyx  spraying  is  governed,  not  by  the  calendar,  but  by 
the  development  of  the  blossoms.  With  the  walnut,  the  nuts  should 
be  as  large  as  possible  at  the  time  of  spraying,  but  the  proper  size  of 
the  nut  is  not  so  important  as  is  the  proper  condition  of  the  calyx  in 
the  apple. 

At  Carpinteria  the  time  for  the  applications  should  be  from  about 
the  first  or  second  week  of  June  to  the  first  of  July. 


SUMMARY 

The  codling  moth  is  an  important  pest  of  walnuts  in  certain  limited 
sections  of  the  walnut-growing  area  of  California.  It  is  found  spar- 
ingly, however,  over  a  large  area.  In  France  and  South  Africa,  also, 
walnuts  are  sometimes  infested. 

The  highest  infestation  noted  in  any  particular  orchard  during 
the  years  1919  to  1925  was  37  per  cent. 

The  codling  moth  which  attacks  the  walnut  is  the  same  insect  that 
is  universally  known  to  attack  the  apple. 

The  life  history  of  the  insect  is  similar  in  all  important  respects  to 
that  of  the  same  insect  when  living  in  the  apple  in  the  same  locality. 

The  larvae  begin  to  enter  the  nuts  as  early  as  the  middle  of  May, 
but  do  not  enter  in  maximum  numbers  until  the  second  or  third  week 
in  June  in  the  Santa  Ana  district  and  from  the  third  week  of  June 
to  the  first  week  of  July  at  Carpinteria ;  hence,  the  time  of  application 
in  seasons  of  average  temperatures  is  during  the  last  week  of  May  and 
the  first  two  weeks  of  June  at  Santa  Ana,  and  a  little  later  in  the 
Carpinteria  district. 

Spraying  with  basic  arsenate  of  lead  is  the  most  satisfactory 
method  of  control.  Dusts  containing  15  per  cent  of  basic  arsenate  of 
lead  may  also  be  employed,  but  the  data  obtained  in  this  investigation 
show  that  the  poison  applied  as  a  dust  is  not  so  effective  as  when 
applied  as  a  spray. 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 


Xo. 

253.   Irrigation   and   Soil   Conditions   in  the 
Sierra   Nevada   Foothills,    California. 

261.  Melaxuma    of    the    Walnut,     "Juglans 

regia." 

262.  Citrus   Diseases   of   Florida    and   Cuba 

Compared  with  Those  of  California. 

263.  Size   Grades   for  Ripe   Olives. 

268.   Growing  and  Grafting  Olive  Seedlings. 
273.   Preliminary  Report  on  Kearney  Vine- 
yard   Experimental   Drain. 

275.  The     Cultivation     of     Belladonna     in 

California. 

276.  The  Pomegranate. 

277.  Sudan    Grass. 

278.  Grain    Sorghums. 

279.  Irrigation   of   Rice   in    California. 

280.  Irrigation    of    Alfalfa    in    the    Sacra- 

mento Valley. 
283.  The   Olive   Insects  of  California. 
285.  The  Milk   Goat   in   California. 
294.  Bean   Culture   in    California. 
304.  A  Study  of  the  Effects  of  Freezes  on 

Citrus    in    California. 
310.   Plum    Pollination. 

312.  Mariout   Barley. 

313.  Pruning      Young      Deciduous      Fruit 

Trees. 
319.   Caprifigs    and    Caprification. 

324.  Storage  of   Perishable  Fruit  at   Freez- 

ing Temperatures. 

325.  Rice     Irrigation     Measurements      and 

Experiments    in    Sacramento    Valley, 

1914-1919. 
328.  Prune    Growing   in    California. 
331.  Phylloxera-Resistant    Stocks. 

334.  Preliminary    Volume    Tables    for    Sec- 

ond-Gro-w^h   Redwood. 

335.  Cocoanut    Meal    as    a    Feed    for   Dairy 

Cows   and    Other   Livestock. 

339.  The    Relative    Cost    of    Making    Logs 

from   Small   and  Large  Timber. 

340.  Control     of     the     Pocket     Gopher     in 

California. 

343.  Cheese    Pests    and    Their    Control. 

344.  Cold    Storage    as    an   Aid  to   the   Mar- 

keting of  Plums. 

346.  Almond    Pollination. 

347.  The  Control  of  Red  Spiders  in  Decid- 

uous Orchards. 

348.  Pruning  Young  Olive  Trees. 

349.  A     Study    of     Sidedraft    and    Tractor 

Hitches. 

350.  Agriculture      in      Cut-over      Redwood 

Lands. 

352.  Further  Experiments  in  Plum  Pollina- 

tion. 

353.  Bovine   Infectious   Abortion. 

354.  Results  of  Rice  Experiments  in   1922. 

357.  A    Self-mixing    Dusting    Machine    for 

Applying      Dry      Insecticides       and 
Fungicides. 

358.  Black     Measles,     Water    Berries,     and 

Related  Vine  Troubles. 

359.  Fruit   Beverage   Investigations. 

361.  Preliminary    Yield    Tables    for    Second 

Growth   Redwood. 

362.  Dust  and  the  Tractor  Engine, 


BULLETINS 
No. 


363. 

364, 

365. 
366. 

367. 

368. 

369. 

370. 
371. 

372. 

373, 
374. 

375. 

376. 

377. 
379. 
380. 

381. 

382. 

383. 

384. 


385. 
386. 

387. 
388. 

389. 
390. 

391. 

392. 
394. 

395. 
396. 

397. 

398. 
399. 


400. 


The  Pruning  of  Citrus  Trees  in  Cali- 
fornia. 

Fungicidal  Dusts  for  the  Control  of 
Bunt. 

Avocado  Culture  in  California, 

Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Methods  of  Harvesting  and  Irrigation 
in   Relation  of  Mouldy  Walnuts. 

Bacterial  Decomposition  of  Olives  dur- 
ing  Pickling. 

Comparison  of  Woods  for  Butter 
Boxes. 

Browning  of  Yellow  Newtown  Apples. 

The  Relative  Cost  of  Yarding  Small 
and   Large   Timber. 

The  Cost  of  Producing  Market  Milk  and 
Butterfat  on  246  California  Dairies. 

Pear    Pollination. 

A  Survey  of  Orchard  Practices  in  the 
Citrus  Industry  of  Southern  Cali- 
fornia. 

Results  of  Rice  Experiments  at  Cor- 
tena,    1923. 

Sun-Drying  and  Dehydration  of  Wal- 
nuts. 

The   Cold    Storage  of   Pears. 

Walnut   Culture   in   California. 

Growth  of  Eucalyptus  in  California 
Plantations. 

Growing  and  Handling  Asparagus 
Crowns. 

Pumping  for  Drainage  in  the  San 
Joaquin    Valley,    California. 

Monilia  Blossom  Blight  (Brown  Rot) 
of  Apricot. 

A  Study  of  the  Relative  Values  of  Cer- 
tain Succulent  Feeds  and  Alfalfa 
Meal  as  Sources  of  Vitamin  A  for 
Poultry. 

Pollination    of    the    Sweet    Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig   Smut. 

The  Principles  and  Practice  of  Sun- 
drying  Fruit. 

Berseem  or   Egyptian    Clover. 

Harvesting  and  Packing  Grapes  in 
California. 

Machines  for  Coating  Seed  Wheat  with 
Copper    Carbonate    Dust. 

Fruit    Juice    Concentrates. 

Cereal  Hay  Production  in  California. 
Feeding  Trials  with  Cereal  Hay. 

Bark   Diseases   of   Citrus  Trees. 

The    Mat    Bean    (Phaseolus    aconilifo- 

lius). 
Manufacture    of  Roquefort  Type  Cheese 
from   Goat's   Milk, 

Orchard  Heating  in  California. 

The  Blackberry  Mite,  the  Cause  of 
Redberry  Disease  of  the  Himalaya 
Blackberry,    and   its   Control. 

The  Utilization  of  Surplus  Plums. 


No. 

87.  Alfalfa. 
113.   Correspondence  Courses  in  Agriculture. 
117.  The    Selection    and    Cost    of    a    Small 

Pumping   Plant. 
127.   House    Fumigation. 
129.  The   Control  of   Citrus   Insects. 
136.   Melilotus    indica    as    a    Green-Manure 
Crop  for  California. 


CIRCULARS 
No. 


144.   Oidium    or    Powdery    Mildew    of    the 
Vine. 

151.  Feeding  and   Management  of   Hogs. 

152.  Some  Observations  on  the  Bulk  Hand- 

ling  of    Grain    in    California. 

154.  Irrigation   Practice   in   Growing   Small 

Fruit    in    California. 

155.  Bovine  Tuberculosis. 


CIRCULARS — (Continued) 


No. 

157. 

160. 

164. 

166. 

167. 

170. 

173. 

178. 
179. 

184. 
190. 
199. 
202. 

20?,. 
209. 
210. 
212. 
214. 

215. 
217. 

220. 
228. 
2.30. 

231. 
232. 

233. 
234. 

235. 

236. 


238. 
239. 

240. 

241. 

242. 
243. 

244. 
245. 
247. 
248. 

249. 
250. 

251. 


252. 
253. 
254. 

255. 


Control  of  the  Pear  Scab. 

Lettuce  Growing  in  California. 

Small  Fruit  Culture  in   California. 

The   County  Farm  Bureau. 

Feeding    Stuffs    of   Minor    Importance. 

Fertilizing  California  Soils  for  the 
1918   Crop. 

The  Construction  of  the  Wood-Hoop 
Silo. 

The   Packing  of  Apples   in   California. 

Factors  of  Importance  in  Producing 
Mi]k  of  Low  Bacterial   Count. 

A    Flock   of    Sheep   on   the   Farm. 

Agriculture  Clubs  in   California. 

Onion    Growing   in    California. 

County  Organizations  for  Rural  Fire 
Control. 

Peat   as    a   Manure    Substitute. 

The  Function  of  the   Farm   Bureau. 

Suggestions  to  the  Settler  in  California. 

Salvaging    Rain-Damaged    Prunes. 

Seed  Treatment  for  the  Prevention  of 
Cereal  Smuts. 

Feeding  Dairy  Cows  in  California. 

Methods  for  Marketing  Vegetables  in 
California. 

Unfermented   Fruit  Juices. 

Vineyard   Irrigation  in   Arid  Climates. 

Testing  Milk,  Cream,  and  Skim  Milk 
for   Butterfat. 

The    Home    Vineyard. 

Harvesting  and  Handling  California 
Cherries    for    Eastern    Shipment. 

Artificial    Incubation. 

Winter  Injury  to  Young  Walnut  Trees 
during  1921-22. 

Soil  Analysis  and  Soil  and  Plant 
Inter-relations. 

The  Common  Hawks  and  Owls  of 
California  from  the  Standpoint  of 
the  Rancher. 

Directions  for  the  Tanning  and  Dress- 
ing of   Furs. 

The  Apricot  in  California. 

Harvesting  and  Handling  Apricots 
and  Plums  for  Eastern   Shipment. 

Harvesting  and  Handling  Pears  for 
Eastern   Shipment. 

Harvesting  and  Handling  Peaches  for 
Eastern   Shipment. 

Poultry  Feeding. 

Marmalade  Juice  and  Jelly  Juice  from 
Citrus   Fruits. 

Central  Wire  Bracing  for  Fruit  Trees. 

Vine   Pruning   Systems. 

Colonization    and    Rural    Development. 

Some  Common  Errors  in  Vine  Prun- 
ing and  Their  Remedies. 

Replacing  Missing  Vines. 

Measurement  of  Irrigation  Water  on 
the  Farm. 

Recommendations  Concerning  the  Com- 
mon Diseases  and  Parasites  of 
Poultry  in   California. 

Supports  for  Vines. 

Vineyard  Plans. 

The  Use  of  Artificial  Light  to  Increase 
Winter    Egg    Production. 

Leguminous  Plants  as  Organic  Fertil- 
izer   in    California    Agriculture. 


No. 

256.  The    Control   of  Wild   Morning   Glory. 

257.  The  Small-Seeded  Horse  Bean. 

258.  Thinning   Deciduous    Fruits. 

259.  Pear  By-products. 

260.  A  Selected  List  of  References  Relating 

to  Irrigation  in  California. 

261.  Sewing  Grain  Sacks. 

262.  Cabbage  Growing  in   California. 

263.  Tomato  Production  in  California. 

264.  Preliminary      Essentials      to      Bovine 

Tuberculosis  Control. 

265.  Plant   Disease   and   Pest   Control. 

266.  Analyzing     the     Citrus     Orchard     by 

Means   of    Simple   Tree   Records. 

267.  The  Tendency  of  Tractors  to   Rise  in 

Front;    Causes   and   Remedies. 

268.  Inexpensive  Labor-saving  Poultry  Ap- 

pliances. 

269.  An  Orchard  Brush  Burner. 

270.  A  Farm  Septic  Tank. 

271.  Brooding    Chicks    Artificially. 

272.  California  Farm  Tenancy  and  Methods 

of  Leasing. 

273.  Saving  the   Gophered  Citrus  Tree. 

274.  Fusarium  Wilt  of  Tomato  and  its  Con- 

trol by  Means  of  Resistant  Varieties. 

275.  Marketable        California        Decorative 

Greens. 

276.  Home   Canning. 

277.  Head,    Cane,    and   Cordon   Pruning  of 

Vines. 

278.  Olive  Pickling  in  Mediterranean  Coun- 

tries. 

279.  The  Preparation  and  Refining  of  Olive 

Oil   in    Southern   Europe. 

281.  The  Results  of  a  Survey  to  Determine 

the  Cost  of  Producing  Beef  in  Cali- 
fornia. 

282.  Prevention  of  Insect  Attack  on  Stored 

Grain. 

283.  Fertilizing  Citrus  Trees  in  California. 

284.  The  Almond   in   California. 

285.  Sweet  Potato  Production  in  California. 

286.  Milk  Houses  for  California  Dairies. 

287.  Potato   Production   in   California. 

288.  Phylloxera  Resistant  Vineyards. 

289.  Oak  Fungus  in  Orchard  Trees. 

290.  The  Tangier  Pea. 

291.  Blackhead   and   Other   Causes  of  Loss 

of  Turkeys  in   California. 

292.  Alkali  Soils. 

293.  The    Basis    of    Grape    Standardization. 

294.  Propagation   of   Deciduous   Fruits. 

295.  The   Growing   and   Handling  of   Head 

Lettuce  in   California. 

296.  Control     of     the     California     Ground 

Squirrel. 

297.  A  Survey  of  Beekeeping  in  California; 

The  Honeybee  as  a  Pollinizer. 

298.  The    Possibilities    and    Limitations    of 

Cooperative   Marketing. 

299.  Poultry   Breeding   Records. 

300.  Coccidiosis  of  Chickens. 

301.  Buckeye  Poisoning  of  the  Honey  Bee. 

302.  The   Sugar  Beet   in   California. 

303.  A  Promising  Remedy  for  Black  Measles 

of  the  Vine. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 

10m-4,'20 


